Summary: Pancreatic ductal adenocarcinoma (PDAC) remains a deadly disease in urgent need of newer therapeutic modalities. PDAC tumors are very heterogeneous carrying alterations in many critical pathways and require a broad form of therapy that can activate multiple tumor suppressor proteins (TSPs) simultaneously. We have shown that in PDAC over-expression of the nuclear exporter protein Exportin 1 (XPO1) leads to functional inactivation of TSPs (such as FOXO3a, p27, Par-4) through their mislocalization. We were the first to demonstrate that inhibition of XPO1 by CRISPR/Cas9 validated Selective Inhibitor of Nuclear Export (SINE) selinexor and analogs can restore the anti-tumor function of multiple TSPs leading to PDAC cell death and tumor inhibition in orthotopic models. More significantly, our findings show that SINE synergize with gemcitabine (GEM) and nab-paclitaxel leading to enhanced PDAC growth inhibition, apoptosis, reversal of epithelial-to-mesenchymal transition (EMT) and spheroid disintegration of PDAC derived cancer stem cells (CSCs). The observed synergy was due in part to enhanced nuclear localization of TSPs and suppression of CSC and EMT markers. Pathway analysis showed enhancement in cell death signaling and suppression of CSC sustaining networks. Most importantly we observed activation of fibroblast specific cell death pathways highlighting an as of yet unexplored role of XPO1 in sustaining fibroblast growth that is recognized to support high desmoplastic reaction (DR) in PDAC. Our multi-model pre-clinical work has led to a Phase Ib/II clinical study involving GEM-nab-paclitaxel-selinexor for metastatic PDAC (NCT02178436). In this proposal we hypothesize that XPO1 inhibition will enforce the nuclear retention of TSPs, restore their anti- tumor function leading to enhancement of cytotoxic efficacy of GEM-nab-paclitaxel in PDAC. To validate our hypothesis, we propose to integrate high-throughput RNA-Seq and SILAC-MS methodologies in primary cellular and transgenic mice models and in a Phase Ib/II trial combining selinexor with Gem-nab-paclitaxel in PDAC patients. We anticipate that our holistic analyses will, for the first time, delineate the impact of XPO1 inhibition in re-programming of PDAC CSC and DR networks that leads to the enhancement in the efficacy of GEM-nab-paclitaxel in tumors. In Aim1 we will demonstrate in vitro synergy between GEM-nab-paclitaxel and selinexor in primary PDAC models using high-throughput methodologies. In Aim2 we will demonstrate the efficacy and synergy of GEM-nab-paclitaxel-selinexor in LSL-KrasG12D/+;LSL-Trp53R172H/+;Pdx-1-Cre mice model. These studies will identify sensitivity and/or resistance markers that will support our phase Ib/II trial in Aim3 in which we intend to determine the safety and efficacy of selinexor when combined with GEM-nab- paclitaxel in patients with metastatic PDAC. Biopsies from this trial will be used to validate locked pharmacodynamic markers of selinexor target engagement in patients. Clinical Impact: The successful completion our studies will bring forward a new therapy to improve the survival of patients with PDAC.